1. Field of the Invention
The present invention relates to a sound-absorbing multi-layer structure for noise reduction, having at least one structural part which is capable of oscillating, preferably of sheet metal or plastic, and an oscillation-absorbing sheet, as well as an especially suitable type of oscillation-absorbing damping sheet for use in this multi-layer structure.
Such sound-absorbing multi-layer structures are found essentially in automobiles, wherein floors, dashboards, doors, roofs and so forth are covered in order to reduce the noise level produced in each of these auto body parts. Measures for the reduction of sound conveyance are particularly important since the negative influences arising from noise are now recognized as leading to passenger discomfort, such as headaches, pounding heartbeat or high blood pressure. Today's automobile industry thus strives to reduce the vehicular noise level as much as possible.
2. Description of the Prior Art
Known measures for reducing of the noise level produced by vibrating automobile body parts are limited to reinforcing and damping the auto body parts in question and to apply additional sound insulation. The known sound-absorbing multi-layer structures consist essentially of a body part and a flex-resistant, dissipative sheet, adhering thereto by means of an adhesive, by being fused thereon. Traditional sound-insulating layers, such as a decorative or a carpet layer, are overlayered. The flex-resistant damping sheets which are used are known to those skilled in the art under various trade names, for instance, Bitumenfolie X999/UKN.
These conventional flex-resistant damping sheets include various properties which are disadvantageous when the damping sheet is in use. On the one hand, application of the differently trimmed and shaped insulation sheets requires both considerable space along the manufacturing assembly line and also costly logistics. On the other hand, during trimming and with the processing, these damping sheets are inclined to peel or break off in bits, forming crumbly lumps. These lumps contaminate the immersion baths used in the finishing of the vehicles, especially paint baths, in an intolerable manner and cause additional cleaning measures to be required, which increase the manufacturing cost.
Another considerable drawback of these flex-resistant damping sheets also lies in the temperature-dependency of their material properties.